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(.module:
[library
[lux #*
[abstract
[monad (#+ do)]]
[control
[pipe (#+ if>)]
["." io (#+ IO)]
["." try (#+ Try)]
["." exception (#+ exception:)]]
[data
[text
["%" format (#+ format)]]
[collection
["." queue (#+ Queue)]]]
[math
[number
["n" nat]
["i" int]]]
[type
abstract
["." refinement]]]]
[//
["." atom (#+ Atom)]
["." async (#+ Async Resolver)]])
(type: State
{#max_positions Nat
#open_positions Int
#waiting_list (Queue (Resolver Any))})
(abstract: #export Semaphore
(Atom State)
{#.doc "A tool for controlling access to resources by multiple concurrent processes."}
(def: most_positions_possible
(.nat (\ i.interval top)))
(def: #export (semaphore initial_open_positions)
(-> Nat Semaphore)
(let [max_positions (n.min initial_open_positions
..most_positions_possible)]
(:abstraction (atom.atom {#max_positions max_positions
#open_positions (.int max_positions)
#waiting_list queue.empty}))))
(def: #export (wait semaphore)
{#.doc (doc "Wait on a semaphore until there are open positions."
"After finishing your work, you must 'signal' to the semaphore that you're done.")}
(Ex [k] (-> Semaphore (Async Any)))
(let [semaphore (:representation semaphore)
[signal sink] (: [(Async Any) (Resolver Any)]
(async.async []))]
(exec (io.run
(with_expansions [<had_open_position?> (as_is (get@ #open_positions) (i.> -1))]
(do io.monad
[[_ state'] (atom.update (|>> (update@ #open_positions dec)
(if> [<had_open_position?>]
[]
[(update@ #waiting_list (queue.push sink))]))
semaphore)]
(with_expansions [<go_ahead> (sink [])
<get_in_line> (in false)]
(if (|> state' <had_open_position?>)
<go_ahead>
<get_in_line>)))))
signal)))
(exception: #export (semaphore_is_maxed_out {max_positions Nat})
(exception.report
["Max Positions" (%.nat max_positions)]))
(def: #export (signal semaphore)
{#.doc (doc "Signal to a semaphore that you're done with your work, and that there is a new open position.")}
(Ex [k] (-> Semaphore (Async (Try Int))))
(let [semaphore (:representation semaphore)]
(async.future
(do {! io.monad}
[[pre post] (atom.update (function (_ state)
(if (i.= (.int (get@ #max_positions state))
(get@ #open_positions state))
state
(|> state
(update@ #open_positions inc)
(update@ #waiting_list queue.pop))))
semaphore)]
(if (is? pre post)
(in (exception.except ..semaphore_is_maxed_out [(get@ #max_positions pre)]))
(do !
[_ (case (queue.peek (get@ #waiting_list pre))
#.None
(in true)
(#.Some sink)
(sink []))]
(in (#try.Success (get@ #open_positions post)))))))))
)
(abstract: #export Mutex
Semaphore
{#.doc "A mutual-exclusion lock that can only be acquired by one process at a time."}
(def: #export (mutex _)
{#.doc (doc "Creates a brand-new mutex.")}
(-> Any Mutex)
(:abstraction (semaphore 1)))
(def: acquire
(-> Mutex (Async Any))
(|>> :representation ..wait))
(def: release
(-> Mutex (Async Any))
(|>> :representation ..signal))
(def: #export (synchronize mutex procedure)
{#.doc (doc "Runs the procedure with exclusive control of the mutex.")}
(All [a] (-> Mutex (IO (Async a)) (Async a)))
(do async.monad
[_ (..acquire mutex)
output (io.run procedure)
_ (..release mutex)]
(in output)))
)
(def: #export limit
{#.doc (doc "Produce a limit for a barrier.")}
(refinement.refinement (n.> 0)))
(type: #export Limit
{#.doc (doc "A limit for barriers.")}
(:~ (refinement.type limit)))
(abstract: #export Barrier
{#limit Limit
#count (Atom Nat)
#start_turnstile Semaphore
#end_turnstile Semaphore}
{#.doc "A barrier that blocks all processes from proceeding until a given number of processes are parked at the barrier."}
(def: #export (barrier limit)
(-> Limit Barrier)
(:abstraction {#limit limit
#count (atom.atom 0)
#start_turnstile (..semaphore 0)
#end_turnstile (..semaphore 0)}))
(def: (un_block times turnstile)
(-> Nat Semaphore (Async Any))
(loop [step 0]
(if (n.< times step)
(do async.monad
[outcome (..signal turnstile)]
(recur (inc step)))
(\ async.monad in []))))
(template [<phase> <update> <goal> <turnstile>]
[(def: (<phase> (^:representation barrier))
(-> Barrier (Async Any))
(do async.monad
[#let [limit (refinement.un_refine (get@ #limit barrier))
goal <goal>
[_ count] (io.run (atom.update <update> (get@ #count barrier)))
reached? (n.= goal count)]]
(if reached?
(..un_block (dec limit) (get@ <turnstile> barrier))
(..wait (get@ <turnstile> barrier)))))]
[start inc limit #start_turnstile]
[end dec 0 #end_turnstile]
)
(def: #export (block barrier)
{#.doc (doc "Wait on a barrier until all processes have arrived and met the barrier's limit.")}
(-> Barrier (Async Any))
(do async.monad
[_ (..start barrier)]
(..end barrier)))
)
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